1. Field of the Invention
The present invention relates to a mobile radio telephone system and, particularly, to a mobile radio telephone system in which a service area is constructed with a plurality of base stations and a mobile telephone terminal performs a communication with one or more of the base stations, which are selected thereby, as the other side of the communication.
2. Description of the Related Art
In a mobile radio telephone system, it is generally impossible for one side of a communication to determine a location of a mobile telephone terminal which is the other side of the communication since the latter terminal may move. In order to solve such problem, for example, Japanese Patent Application Laid-open Nos. H-328432 and S64-71226 disclose mobile radio telephone systems in each of which one side of a communication can know an area in which a mobile telephone terminal which is the other side of the communication is currently located.
In detail, the mobile radio telephone system disclosed in Japanese Patent Application Laid-open No. H5-328432, which will be referred to as "first prior art", hereinafter, is a cordless telephone system including at least one telephone connecting device for connecting a plurality of cordless telephone sets each having a display device. The mobile telephone system includes a position registration information memory portion and an inter-call processing portion and, when an inter-call is performed by one of the cordless telephone sets to another, the position registration information memory portion is referred to obtain a positional information of the connecting device used by the calling side cordless telephone set and the called side cordless telephone set and the positional information of the calling and called sides thus obtained is transmitted to the called side cordless telephone set and the calling side cordless telephone set as data to be displayed on display portions of the called and calling side cordless telephone sets, respectively, so that the positional information of one of the two cordless telephone sets is displayed on the display device of the other cordless telephone set, or vice versa.
On the other hand, the mobile radio telephone system disclosed in Japanese Patent Application No. S64-71226, which will be referred to as "second prior art", hereinafter, is provided on an exchanger side with a position display device for displaying a positional information of mobile radio telephone terminals. That is, in this mobile radio telephone system, the automatic position detecting function which is inherent to the mobile radio telephone system is utilized. The exchanger connected to a plurality of base stations through radio interface circuits stores positional information of respective mobile radio telephone terminals existing in radio zones of the base stations and displays the information on the position display devices thereof.
Further, Japanese Patent Application Laid-open No. H1-297920 discloses a service system for informing a location of a mobile radio telephone in which an area in which a mobile radio telephone exists is informed by means of audio sound, which will be referred to as "third prior art", hereinafter.
However, in the first prior art, it is only possible to display the positional information of one of the cordless telephones on the display device of the other cordless telephone under the limited condition of the intercommunication between the cordless telephone sets. In the second prior art, it is impossible to display a position on the side of the mobile telephone terminal since the position display device is provided on the exchanger.
In any of the first, second and third prior arts, it is impossible for a mobile telephone terminal to confirm a position of a base station, a distance from the mobile telephone terminal to the base station and a direction of the base station seen from the mobile telephone terminal and to inform the distance and the direction of the base station related to the mobile telephone terminal to the other telephone terminal, although it is possible to confirm an area in which the mobile telephone terminal exists.